1. Field of the Invention
This invention relates to a recording/reproducing apparatus and a reproducing apparatus suitable when used in, e.g., a digital video tape recorder equipment, etc.
2. Description of the Related Arts
Nowadays, digital signal processing technology is being remarkably developed in broadcast using ground wave, satellite broadcast, cable television (CATV), telephone line and the like for transmitting picture signals and/or audio signals, because the transmission band is limited. There is proposed, in order to effectively utilize such limited transmission band, a compression transmission broadcasting system to compress not only picture data and audio data but also the time base by using digital signal processing technology to transmit picture/audio data which has undergone data compression and time base compression.
A compression transmitting apparatus for realizing such compression transmission broadcasting system is composed, of as shown in FIG. 6, a MPEG (Moving Picture Expert Group) encoder 100, a time base compressing circuit 101, and a frame forming (encoding) and modulating circuit 102.
The MPEG encoder 100 adaptively carries out switching between intraframe coding processing and interframe coding processing for compressing the picture data to conduct coding, and carries out motion compensating predictive coding in the interframe coding processing.
In the above example, the MPEG encoder 100 divides one picture comprised of, e.g., one frame or one field into so called macroblocks comprised of, e.g., 16 pixels.times.16 pixels to carry out motion compensating predictive coding in units of these macroblocks.
In more practical sense, as shown in FIG. 5, as the processing of the first stage, motion compensating predictive coding is successively implemented to Predictive-coded pictures (hereinafter simply referred to as P pictures) jumping over a predetermined number of pictures successive in point of time.
As the processing of the second stage, motion compensating predictive coding is implemented to Bidirectionally predictive-coded pictures (hereinafter simply referred to as B pictures) put between the P pictures or Intra-coded pictures (hereinafter simply referred to as I pictures) by using P picture or I picture before and after. It is to be noted that I picture is a picture subject to intraframe coding processing, i.e., a picture which is not subject to motion compensating predictive coding.
The MPEG encoder 100 carries out compression of picture data every predetermined block in this way to thereby allow the transmission rate of picture/audio data of the picture data and audio data obtained from an audio encoder (not shown) to be, e.g., 1.5 Mbps to deliver it to the time base compressing circuit 101.
The time base compressing circuit 101 implements a predetermined time base compression processing to picture/audio data every block to which the data compression processing has been implemented to thereby allow the transmission rate of the picture/audio data to be, e.g., 15 Mbps to deliver it to the frame forming and modulating circuit 102. Namely, since picture/audio data of 1.5 Mbps is compressed in a direction of the time base and is resultantly outputted as data of 15 Mbps, the time base is compressed to a degree ten times greater than that when no time base compression processing is implemented.
The frame forming and modulating circuit 102 implements frame formation processing for forming a transmission unit (frame) of picture data every block to which the data compression processing and the time base compression processing have been implemented and adding an error correcting code thereto. This circuit 102 further implements a predetermined modulation processing thereto to thereby form picture data having a transmission rate of, e.g., 25 Mbps to output it through transmission cable 103.
By implementing such processing, it is possible to transfer picture/audio data by effectively utilizing a limited frequency band. For example, it is possible to transfer cinema-like picture/audio data of two hours in 12 minutes (time which is one tenth of 120 minutes (two hours)).
It is to be noted that in the case of multiplexing channels, a multiplexer is provided at the preceding stage or the succeeding stage of the frame forming and modulating circuit 102. By this multiplexer, picture/audio data as described above are multiplexed.
In this multiplexing, if, e.g., transmission band of cable line 103 is 25 Mbps, it is possible to multiplex the picture/audio data of about 10 channels (1.5 Mbps.times.10 channels+redundancy=25 Mbps by addition of parity or modulation).
However, if time base expansion processing and data expansion processing, etc. are implemented to picture/audio data transmitted from the compression transmitting apparatus as described above so that original picture/audio data results to record it, a quantity of data to be recorded is increased. For example, there may take place an unreasonableness such that recording time as long as two hours is required while transmission time is 12 minutes.
Further problem is that since picture/audio data is transmitted in the state where complicated compression processing as described above are implemented thereto, a special decoder device is required for reproducing such data.